A fingerprint is an optimal biometric password with uniqueness. With the maturation and popularization of identification apparatuses and technologies, in addition to access control for house protection, personal documents, ID authentication in payment systems, and places where strict access control is required, recently, fingerprint sensing devices have also been commonly used in mobile devices for application identification.
For traditional fingerprint sensing devices, backlight is transmitted through a photosensitive element to reach a finger, where a fingerprint of the finger reflects the light with crests and troughs. The photosensitive element receives the reflected light to detect the difference between the crests and the troughs, thereby sensing the fingerprint. However, traditional fingerprint sensing devices have a problem of image overexposure under strong outdoor light. In particular, due to a wavelength of sunlight above 600 nm, too much light is transmitted through the finger, causing the photoelectric current of the photosensitive element to be over-saturated. In other words, if a mobile device with traditional fingerprint sensing devices is used outdoors, it is usually difficult to read the images of fingerprints. Accordingly, how to solve the problem of existing fingerprint sensing devices not being useful under strong outdoor light is an issue to be addressed at present.